This invention relates to the use of fluoropolymers and methods of applying fluoropolymers in making components for optical applications. In particular, the invention relates to copolymer compositions and methods for micromolding and microcontact lithographic printing.
Polymeric large core waveguides for optical interconnects have been fabricated using rubber molding processes. Large core waveguides are prepared using photoresist patterning processes in a master fabrication procedure.
In the electronics and optical fabrication technologies, optical interconnects have been used in backplane interconnections, board to board interconnections, clock distribution, and a variety of other applications. In particular, lithographic processes have been used because such processes are generally suitable for mass production, are usually insensitive to the polymer selection, and are of relatively low cost. Molding processes have in the past relied on micro-fabrication by traditional lithography.
More recently, xe2x80x9csoft lithographicxe2x80x9d techniques have been used to microfabricate an assortment of structures. The micromolding procedure usually involves at least three steps. First, a silicon master is fabricated. Next, a mold is made or replicated from the silicon master. Finally, a transferring process is used to transfer or stamp the replication of the mold by micro-contact printing onto a polymeric material. In master fabrication, a two step baking process of a thick photoresist is used. A polydimethylsiloxane (PDMS) lastomer, which is a type of silicone rubber, is used as the mold. Then a polymer material is replicated from the mold to produce a polymeric optical wave guide which is useful for a variety of applications.
A process for producing polymeric optical wave guides without first preparing a mold would be desirable. However, in practice it has been recognized that physical properties of the polymer used in the processes are very important to the success of the process itself, and to the performance of the optical device in terms of its refractive index.
It has also been recognized in the industry that a need exists for polymeric optical devices which show a fine resolution, thereby enabling the manufacture of smaller components.
At least one publication has recognized that perfluorocyclobutane (PFCB)-containing polymers may be used as a polymer in the fabrication of polymeric large core wave guides for optical interconnects using a rubber molding process. Byung Tak Lee, et al. xe2x80x9cFabrication of Polymeric Large Core Wave Guides for Optical Interconnects Using a Rubber Molding Processxe2x80x9d, IEEE Photonics Technology Letters, Volume 12, Number 1 (January, 2000). However, this publication does not purport to analyze a full range of PFCB compounds to determine which specific compounds generate tunable optical (i.e. refractive index and Tg) performance in the process.
Compounds that may be used to prepare a polymer which is capable of simplifying the process of replication while at the same time providing suitable optical and light transmitting qualities in a final optical device would be desirable. Furthermore, polymers that may be used in a higher resolution device which is capable of providing a diffraction pattern with a narrow line width would be desirable.
The invention comprises compositions and methods of application of compounds which include fluoropolymers consisting of alternating perfluorocyclobutane and aryl ether linkages. These compositions possess the mechanical, thermal and structural properties and the desired optical clarity required for the manufacture of optical waveguides and the like.
In some applications of the invention, the fluoropolymer may be used both as a reinforcing component and as an optical signal carrier in a structural polymer matrix composite. Such composites may provide fully integrated high speed data transmission mediums with switching and routing capabilities. Thermoplastic and thermosetting polymers containing perfluorocyclobutane (PFCB) and arylene ether linkages provide high performance and a multi-functional polymer. PFCB segments may provide improved dielectric insulation, optical clarity, visible and near infrared wavelengths, increased solubility, melt processability and other valuable properties.
In one aspect of the invention, a co-polymer is provided which comprises a poly-aryl ether with perfluorocyclobutyl (PFCB) linkages comprising a chain polymer having the formula: 
In the above polymer, z is generally greater than or equal to 2, and the Ar and Arxe2x80x2 group comprises a substituted or non-substituted aryl which is capable of forming a suitable polymer of both linear thermoplastic and thermosetting types. In some applications of the invention, the aryl group includes multiple aromatic rings attached to the PFCB polymer. For example, any one or more of the following aryl groups may be provided: 
Of course, the above groups may be substituted with other alkyl or organic constituents on the one or more carbons, such as a carbon comprising the ring structure, and the above structures are provided by way of example and not by way of limitation. In some applications, a polymer is provided which is prepared from a trifluorovinyl aromatic ether (TVE). Trifluorovinyl aromatic ether monomer precursors are traditionally prepared in two high yielding steps from commercially available phenolic precursors such as, for example, tris (hydroxyphenyl) ethane, biphenol, bishydroxyphenyl fluorene, or other compounds. Partially inorganic monomers containing siloxane and phosphine oxide groups have also been synthesized using an intermediate strategy involving delivery of a TFVE group intact via Grignard and organo-lithium chemistry.
The invention further comprises a method of making a PFCB polymer film which comprises the steps of providing a silicon master, replicating a PFCB polymer directly from the silicon master, and then curing the polymer. In some cases, the replicating step comprises applying a PFCB liquid polymer into the silicon master. In other applications, the replicating step comprises providing an oligomer or a co-oligomer onto the silicon master. In other applications of the invention, a diffraction device or an optical waveguide may be prepared in which the ridges of the diffraction device are spaced less than 50 xcexcm apart. Further, an optical device may be prepared using the method in which the ridges of the diffraction device are spaced less than 25 xcexcm apart. In other preferred embodiments, the ridges of the diffraction grating or device may be spaced less than 1 xcexcm apart, and in other embodiments as little as 0.5 xcexcm apart.
A method of making a PFCB polymer film or copolymer for variable optical properties, e.g. refractive index is provided which comprises providing a silicon master, replicating a mold from the silicon master, replicating a PFCB polymer from the mold by providing uncured components into the mold, and then curing the components to form a polymer product.
Polymers with a wide range of mechanical, thermal and optical properties may be obtained using the above referenced chemistry. In particular, the refractive indices of the homopolymers or the co-polymers may be provided exactly as designed by careful regulation of monomer choice. Thus the refractive index as a function of wavelength can be precisely controlled. The invention is capable of providing well defined cyclopolymerization mechanisms using PFCB to prepare polymers with tunable thermal and optical properties. For example, random amorphous co-polymers with variable refractive indices, glass transition temperatures, and long term thermal stability above 350xc2x0 C. may be prepared by correct choice of a co-monomer composition. Co-polymers may be prepared by simple melt mixing of variable composition monomer mixtures and heating under appropriate conditions. Using the invention, it is possible under some conditions to provide for precise control of refractive index by the choice of co-monomer which is used. Thus, the thermal cyclopolymerization of aromatic trifluorovinyl ether monomers to perfluorocyclobutane polymers and co-polymers affords high temperature, low transmission loss, and variable refractive index for use in optical telecommunication devices and the like.